Filtration media and methods of preparation

ABSTRACT

Provided are methods of preparing filtration media in which a microporous layer is coated on a temporary carrier substrate and a porous substrate is then laminated to the microporous layer, after or prior to removing the temporary carrier substrate from the microporous layer. Preferably, the microporous layer comprises one or more microporous xerogel layers. Also provided are filtration media prepared by such methods.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/325,074, filed Dec. 20, 2002, which is a division of U.S. patentapplication Ser. No. 09/590,457, filed Jun. 9, 2000, now U.S. Pat. No.6,497,780, which claims priority to U.S. Provisional Patent ApplicationSer. No. 60/139,031, filed Jun. 9, 1999, and also relates to two U.S.patent applications, titled “Capacitors and Methods of Preparation” and“Fuel Cells and Methods of Preparation,” filed on even date herewith,the contents of which related applications are incorporated herein byreference in their entirety for all purposes.

TECHNICAL FIELD

The present invention relates generally to the field of articlescomprising a microporous layer. More particularly, this inventionpertains to methods of preparing an article comprising a microporouslayer in which a microporous layer is coated on a temporary carriersubstrate and a substrate is then laminated to the microporous layer,prior to removing the temporary carrier substrate from the microporouslayer. The present invention also pertains to articles, such aselectrochemical cells, capacitors, fuel cells, ink jet printing media,and filtration media, prepared by such methods.

BACKGROUND

Throughout this application, various publications, patents, andpublished patent applications are referred to by an identifyingcitation. The disclosures of the publications, patents, and publishedpatent applications referenced in this application are herebyincorporated by reference into the present disclosure to more fullydescribe the state of the art to which this invention pertains.

U.S. patent application Ser. No. 08/995,089 titled “Separators forElectrochemical Cells,” filed Dec. 19, 1997, to Carlson et al. of thecommon assignee, describes microporous layers as separators for use inelectrochemical cells in which microporous layers comprise a microporouspseudo-boehmite layer prepared by coating and drying a boehmite sol. Themicroporous pseudo-boehmite separators and methods of preparing suchseparators are described for both free standing separators and as aseparator layer coated directly onto an electrode or another layer ofthe cell.

When a microporous layer, such as a microporous separator layer, iscoated directly onto an electrode, such as onto the cathode, themicroporous separator coating may require a relatively smooth, uniformsurface on the electrode and also may require a mechanically strong andflexible electrode layer. For example, for a microporous pseudo-boehmitelayer having a xerogel structure, these specific electrode surface andlayer properties may be required to prevent excessive stresses andsubsequent cracking of the xerogel layer during drying of thepseudo-boehmite coating on the electrode surface and also duringfabrication and use of electrochemical cells containing thepseudo-boehmite xerogel layer.

Besides separator-coated electrodes and electrochemical cells, a largevariety of other articles comprising a microporous layer may require arelatively smooth, uniform surface on a substrate to which themicroporous layer is to be applied. Also, the substrate may need to bemechanically strong and flexible. For example, for a microporous xerogellayer as used in ink jet printing media, such as described, for example,in U.S. Pat. No. 5,463,178 to Suzuki et al., such smooth, uniform, andother substrate properties may be useful in preventing excessivestresses and subsequent cracking of the xerogel layer, particularly whenits thickness is above 20 microns, and also useful in providingexcellent image quality. Some of the desired substrates in ink jetprinting media, such as canvas, cloth, non-woven fiber substrates, andsome grades of paper, have very rough and non-uniform surfaces and aredifficult to coat with the microporous xerogel layers which typicallyprovide the premium ink jet image quality. One approach to overcome thesurface deficiencies of the substrate is to pre-coat the substrate witha coating layer. This approach may reduce the surface roughness andnon-uniformities, but involves the expense and complexity of anadditional coating step, usually does not fully eliminate the surfacedeficiencies, and may negatively affect the ink jet imaging, such as byinterfering with the microporosity and transport of liquids between thexerogel layer and the rough but porous substrate.

In another approach that may overcome the surface deficiencies of thesubstrate, the ink jet ink-receptive layer may be coated on a temporarycarrier layer to form an ink jet ink printing media for imaging on anink jet printer, as, for example, described in U.S. Pat. Nos. 5,795,425and 5,837,375, both to Brault et al. Then, as part of a two step imagingprocess, the ink jet media is imaged on the ink jet printer followed bylamination of the imaged ink jet ink-receptive layer to a desiredsubstrate and removal of the temporary carrier layer from the ink jetink-receptive layer. This approach has the disadvantage of being atwo-step imaging proess where the user may obtain excellent quality inthe first imaging step, but then, after the effort and expense ofimaging, the quality of the second lamination step may be unacceptable.Also, this two step imaging process requires the user to have theequipment for the second lamination step. It would be advantageous tohave a one step imaging process for ink jet printing on ink jet inkprinting media having rough, non-uniform substrates.

A method for preparing articles, such as electrochemical cells and inkjet printing media, which can avoid the foregoing problems oftenencountered with preparing articles comprising a microporous layer,particularly those comprising a microporous xerogel layer, would be ofgreat value.

SUMMARY OF THE INVENTION

The present invention pertains to methods of preparing an articlecomprising a microporous layer, which methods comprise the steps of (a)coating a microporous layer on a temporary carrier substrate to form amicroporous layer assembly, wherein the microporous layer has a firstsurface in contact with the temporary carrier substrate and has a secondsurface on the side opposite from the temporary carrier substrate; (b)laminating the second surface of the microporous layer to a substrate toform a microporous layer/substrate assembly; and (c) removing thetemporary carrier substrate from the first surface of the microporouslayer to form the article. In a preferred embodiment, the microporouslayer comprises one or more microporous xerogel layers. In oneembodiment, the microporous layer assembly further comprises one or morenon-microporous coating layers, wherein the one or more non-microporouscoating layers are in contact with at least one of the one or moremicroporous xerogel layers of the microporous layer. In one embodiment,one of the one or more microporous xerogel layers of the microporouslayer is coated directly on the temporary carrier substrate. In oneembodiment, one of the one or more non-microporous coating layers of themicroporous layer assembly is coated directly on the temporary carriersubstrate prior to coating the microporous layer, and the microporouslayer is then coated on a surface of the one of the one or morenon-microporous coating layers, which surface is on the side of the oneof the one or more non-microporous coating layers opposite from thetemporary carrier substrate, and further wherein the temporary carriersubstrate is removed in step (c) from a surface of the one of the one ormore non-microporous coating layers, which surface is on the side of theone of the one or more non-microporous coating layers opposite from themicroporous layer. In one embodiment, one of the one or morenon-microporous coating layers of the microporous layer assembly iscoated after step (a) directly on the surface of the microporous layer,which surface is on the side of the microporous layer opposite from thetemporary carrier substrate layer, prior to laminating to the substratein step (b).

In a preferred embodiment, at least one of the one or more microporousxerogel layers comprises a xerogel material selected from the groupconsisting of pseudo-boehmites, zirconium oxides, titanium oxides,aluminum oxides, silicon oxides, and tin oxides. In one embodiment, themicroporous layer comprises a microporous material prepared byvesiculation of an organic polymer layer, and wherein said vesiculationcomprises a step of photolyzing or heating a gas forming compound. Inone embodiment, the gas forming compound is an aromatic diazoniumcompound.

In one embodiment of the methods of preparing an article comprising amicroporous layer of the present invention, the temporary carriersubstrate is a flexible web substrate. Suitable web substrates include,but are not limited to, papers, polymeric films, and metals. In oneembodiment, the flexible web substrate is surface treated with a releaseagent.

In one embodiment, the microporous layer assembly is a cathode/separatorassembly, the substrate is an anode assembly, and the article is anelectrochemical cell. The electrochemical cell may be a primary cell ora secondary cell.

In one embodiment, the microporous layer assembly is an ink jetink-receptive coating assembly, the substrate is a flexible websubstrate, and the article is an ink jet ink printing media.

In one embodiment, the microporous layer assembly is an ultrafiltrationlayer assembly, the substrate is a flexible web substrate, and thearticle is a filtration media.

In one embodiment, the microporous layer assembly is a separatorassembly, the substrate is a first electrode assembly, and the articleis a first electrode/separator assembly. In one embodiment, the methodsfurther comprise the step of combining the first electrode/separatorassembly with a second electrode assembly to prepare an electrochemicalcell, a capacitor, or a fuel cell.

Another aspect of the present invention pertains to an article preparedby the methods of this invention, as described herein. In a preferredembodiment, the article is an ink jet ink printing media.

As will be appreciated by one of skill in the art, features of oneaspect or embodiment of the invention are also applicable to otheraspects or embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a representative process flow diagram with cross-sectionalviews of one embodiment of the methods of preparing an article of thepresent invention, which comprises a non-microporous coating layer step41, a lamination step 60, and a temporary carrier substrate removingstep 70, starting with a microporous layer assembly 15 comprising atemporary carrier layer 2, a non-microporous coating layer 101, and amicroporous layer 102.

FIGS. 2A and 2B show representative process flow diagrams withcross-sectional views of two other embodiments of the methods ofpreparing an article of this invention, which comprises, for FIG. 2A, alamination step 80 prior to the temporary carrier substrate removingstep 70; and which comprises, for FIG. 2B, a lamination coating step 80and a slitting step 95 prior to the temporary carrier substrate removingstep 70, where these steps are done starting with a microporous layerassembly 24 comprising a temporary carrier substrate 2, a microporouslayer 102, and two different non-microporous coating layers 201 and 301.

DETAILED DESCRIPTION OF THE INVENTION

Many microporous coatings, particularly microporous xerogel coatingswhich are typically subject to a high level of stresses and potentialcracking during drying, formation, and mechanical handling of thethree-dimensional gel structure in the microporous layer, are difficultto obtain at the desired quality level when coated on surfaces which arerough and non-uniform or which have poor mechanical strength andflexibility properties. A rough and non-uniform coating surface maycause a wide variation in the thicknesses of microporous coatingsapplied to this surface. Besides possibly causing the formation ofsections of the microporous coating layer which are too thin for thedesired application, these thickness variations may interfere with thedesired level and uniformity of the microporosity and with themechanical strength and cracking resistance of the microporous layer.This is particularly true when the thickness of the microporous coatinglayer is significantly above that needed for the desired application.Also, a coating surface with poor mechanical strength and flexibilitymay induce, for example, stresses, mechanical failure, poor adhesion,and cracking in a microporous layer coated on this surface. Examples ofapplications for microporous coatings, including microporous xerogelcoatings, where a relatively smooth surface and a mechanically stronglayer on which to apply and form the microporous coating would beuseful, include, but are not limited to, microporous separators forcontact to one or more electrodes of an electrochemical cell, capacitor,or fuel cell; microporous ink jet ink-receptive layers for contact to awide variety of rough, uneven support surfaces such as papers, fabrics,canvas, and spun-woven plastics; and microporous filtration layers forcontact to a wide variety of rough, uneven substrates such as papers.For example, for the product application of microporous separatorsinvolving contact to the positive electrode or cathode of anelectrochemical cell, the roughness and non-uniformity of the cathodesurface prior to coating the microporous separator layer on it may bereduced, for example, by calendering the cathode surface or by applyinga thin uniform coating to the cathode surface. However, the reduction ofthe roughness and non-uniformity of the cathode surface by theseapproaches may still not be sufficient and also may not preventundesirable results from poor mechanical strength and flexibility of thecathode and from penetration of the separator coating into porous areasof the cathode during the coating application process.

The present invention overcomes these limitations for preparingmicroporous coatings for a wide variety of applications, such asseparators for use in electrochemical cells, ink jet ink-receptivemedia, filtration materials, and other product applications. One aspectof the present invention pertains to methods of preparing an article,which methods comprise the steps of (a) coating a microporous layer on atemporary carrier substrate, (b) coating any other desired layers indesired coating patterns built up on the surface of the microporouslayer on the side opposite from the temporary carrier substrate, (c)laminating the microporous layer assembly resulting from steps (a) and(b) to a desired substrate, such as an anode assembly comprising ananode active layer, and (d) removing the temporary carrier substratefrom the microporous separator layer before step (c) or, alternatively,after step (c). A lamination process similar to that of step (c) may beutilized in step (b) to coat the microporous layer by a lamination stepof applying an assembly comprising, for example, a cathode active layerof the cathode to the surface of the microporous layer on the sideopposite from the temporary carrier substrate, wherein the cathodeactive layer has a first surface in contact with the surface of themicroporous layer and has a second surface on the side opposite from thetemporary carrier substrate. In one embodiment of the lamination processin step (b), the assembly comprising, for example, the cathode activelayer, further comprises a second temporary carrier substrate, andwherein, subsequent to step (b), there is a step of removing the secondtemporary carrier substrate from the assembly comprising the cathodeactive layer.

The surface of the temporary carrier substrate is selected to have thesmoothness, mechanical strength, flexibility, and porosity propertiesthat are desirable for the preparation of the microporous layer bycoating on the surface of the temporary carrier substrate and to alsohave the suitable release properties for removal of the temporarycarrier substrate. This method of applying a microporous layer to atemporary carrier substrate, subsequent coating and/or lamination of oneor more other layers overlying the microporous layer, and the subsequentremoval of the temporary carrier substrate from the microporous layer isparticularly useful when the microporous layer comprises one or moremicroporous xerogel layers. Besides applications in electrochemicalcells, this method may be readily adapted for a wide variety of otherproduct applications, including ink jet ink-receptive media andfiltration materials, where microporous coating layers may be utilized.

One embodiment of the methods of the present invention is illustrated inFIG. 1. Referring to FIG. 1, in a non-microporous coating step 41, anon-microporous coating layer 103 is coated onto a surface of amicroporous layer assembly 15 comprising a temporary carrier substrate2, a non-microporous coating layer 101, and microporous layer 102,thereby forming microporous layer assembly 18. Next, in a laminationstep 60, a substrate 201 is laminated onto the surface of thenon-microporous coating layer 103 to form microporous layer/substrateassembly 19 comprising temporary carrier substrate 2, non-microporouscoating layer 101, microporous layer 102, non-microporous coating layer103, and substrate 201. Following this step, in a temporary carriersubstrate removing step 70, the temporary carrier substrate 2 is removedfrom the microporous layer 102 of microporous layer/substrate assembly19 to form an article 20 comprising non-microporous coating layer 101,microporous layer 102, non-microporous coating layer 103, and substrate201.

The term “electrochemical cell,” as used herein, pertains to an articlethat produces an electric current through an electrochemical reactionand that comprises a positive electrode or cathode, a negative electrodeor anode, and an electrolyte element interposed between the anode andthe cathode, wherein the electrolyte element comprises a separator layerand an aqueous or non-aqueous electrolyte in pores of the separatorlayer. Electrochemical cells may be primary or secondary cells.

The term “microporous” as used herein, pertains to the material of alayer, which material possesses pores of diameter of about 1 micron orless which are interconnected in a substantially continuous fashion fromone outermost surface of the layer through to the other outermostsurface of the layer. The term “microporous layer” is used herein todescribe a layer, which layer may comprise one or more discrete coatinglayers, where the layer as a whole is microporous. Examples ofmicroporous materials useful in the microporous separator layer of themethods of the present invention include, but are not limited to,inorganic xerogel layers or films, inorganic xerogel layers or filmsfurther comprising an organic polymer, and organic polymer layers orfilms that undergo vesiculation or pore formation upon gas formation,for example, by heating or photoirradiating an aromatic diazoniumcompound or other gas forming compound, as known for example in the artof preparing vesicular microfilm.

The terms “non-microporous layer” and “non-microporous coating layer”are used herein to pertain to a layer, which layer may comprise one ormore discrete coating layers, where the layer as a whole is notmicroporous.

In one embodiment of the methods of preparing an article of thisinvention, the microporous layer comprises one or more microporousxerogel layers. By the terms “xerogel layer” and “xerogel structure,” asused herein, is meant, respectively, a layer of a coating or thestructure of a coating layer in which the layer and structure wereformed by drying a liquid sol or sol-gel mixture to form a solid gelmatrix as, for example, described in Chem. Mater., Vol. 9, pages 1296 to1298 (1997) by Ichinose et al. for coating layers of metal-oxide basedxerogels. Thus, if the liquid of the gel formed in the liquid sol-gelmixture is removed substantially, for example, though formation of aliquid-vapor boundary phase, the resulting gel layer or film is termed,as used herein, a xerogel layer. As the liquid is removed from the gelin the liquid sol-gel mixture by, for example, evaporation, largecapillary forces are exerted on the pores, forming a collapsed structurefor the xerogel layer. The pore sizes of the xerogel layer and structureare very small, having average pore diameters less than 300 nm or 0.3microns.

Thus, the microporous xerogel layer of the methods of this inventioncomprises a dried microporous three-dimensional solid gel network withpores which are interconnected in a substantially continuous fashionfrom one outermost surface of the layer through to the other outermostsurface of the layer. A continuous xerogel coating layer has thematerials of the xerogel in a continuous structure in the coating layer,i.e., the materials are in contact and do not have discontinuities inthe structure, such as a discontinuous layer of solid pigment particlesthat are separated from each other. In contrast, xerogel pigmentparticles may be formed by a xerogel process involving drying a liquidsolution of a suitable precursor to the pigment to form a dried mass ofxerogel pigment particles, which is typically then ground to a finepowder to provide porous xerogel pigment particles. The terms “xerogelcoating” and “xerogel coating layer,” as used herein, are synonymouswith the term “xerogel layer”.

The term “binder,” as used herein, pertains to inorganic or organicmaterials which form a continuous structure or film in a substantiallycontinuous fashion from one outermost surface of a coating layer throughto the other outermost surface of the coating layer. As such, forexample, the xerogel, such as pseudo-boehmite or other metal oxidexerogel, of a xerogel layer is also a binder in addition to having axerogel structure with ultrafine pores.

A wide variety of materials known to form microporous xerogel layerswhen coated on a surface may be used to provide the microporous layersfor the methods of the present invention. Suitable materials for use inthe microporous xerogel layers of the microporous layer of the methodsof the present invention include, but are not limited to,pseudo-boehmites, zirconium oxides, titanium oxides, aluminum oxides,silicon oxides, and tin oxides.

In a preferred embodiment of the methods of preparing an article of thisinvention, the microporous layer comprises one or more microporouspseudo-boehmite layers. Microporous pseudo-boehmite layers for use asseparators in electrochemical cells are described in copending U.S.patent application Ser. Nos. 08/995,089 and 09/215,112, both to Carlsonet al. of the common assignee, the disclosures of which are fullyincorporated herein by reference. The term “pseudo-boehmite,” as usedherein, pertains to hydrated aluminum oxides having the chemical formulaAl₂O₃.xH₂O wherein x is in the range of from 1.0 to 1.5. Terms, as usedherein, which are synonymous with “pseudo-boehmite,” include “boehmite,”“AlOOH,” and “hydrated alumina.” The materials referred to herein as“pseudo-boehmite” are distinct from anhydrous aluminas (Al₂O₃, such asalpha-alumina and gamma-alumina), and hydrated aluminum oxides of theformula Al₂O₃.xH₂O wherein x is less than 1.0 or greater than 1.5.

The amount of the pores in a microporous layer may be characterized bythe pore volume, which is the volume in cubic centimeters of pores perunit weight of the layer. The pore volume may be measured by filling thepores with a liquid having a known density and then calculated by theincrease in weight of the layer with the liquid present divided by theknown density of the liquid and then dividing this quotient by theweight of the layer with no liquid present, according to the equation:${{Pore}\quad{Volume}} = \frac{\left\lbrack {W_{1} - W_{2}} \right\rbrack/d}{W_{2}}$where W₁ is the weight of the layer when the pores are completely filledwith the liquid of known density, W₂ is the weight of the layer with noliquid present in the pores, and d is the density of the liquid used tofill the pores. Also, the pore volume may be estimated from the apparentdensity of the layer by subtracting the reciprocal of the theoreticaldensity of the materials (assuming no pores) comprising the microporouslayer from the reciprocal of the apparent density or measured density ofthe actual microporous layer, according to the equation:${{Pore}\quad{Volume}} = \left( {\frac{1}{d_{1}} - \frac{1}{d_{2}}} \right)$where d₁, is the density of the layer which is determined from thequotient of the weight of the layer and the layer volume as determinedfrom the measurements of the dimensions of the layer, and d₂ is thecalculated density of the materials in the layer assuming no pores arepresent or, in other words, d₂ is the density of the solid part of thelayer as calculated from the densities and the relative amounts of thedifferent materials in the layer. The porosity or void volume of thelayer, expressed as percent by volume, can be determined according tothe equation:${Porosity} = \frac{100\left( {{Pore}\quad{Volume}} \right)}{\left\lbrack {{{Pore}\quad{Volume}} + {1/d_{2}}} \right\rbrack}$where pore volume is as determined above, and d₂ is the calculateddensity of the solid part of the layer, as described above.

In one embodiment, the microporous xerogel layer of the microporouslayer of the methods of the present invention has a pore volume from0.02 to 2.0 cm³/g. In a preferred embodiment, the microporous xerogellayer has a pore volume from 0.3 to 1.0 cm³/g. In a more preferredembodiment, the microporous xerogel layer has a pore volume from 0.4 to0.7 cm³/g.

The microporous xerogel layers of the microporous layer of the methodsof the present invention have pore diameters which range from 0.3microns down to less than 0.002 microns. In one embodiment, themicroporous xerogel layer has an average pore diameter from 0.001microns or 1 nm to 0.3 microns or 300 nm. In a preferred embodiment, themicroporous xerogel layer has an average pore diameter from 0.001microns or 1 nm to 0.030 microns or 30 nm. In a more preferredembodiment, the microporous xerogel layer has an average pore diameterfrom 0.003 microns or 3 nm to 0.010 microns or 10 nm.

One distinct advantage of microporous layers with much smaller porediameters on the order of 0.001 to 0.03 microns is that insolubleparticles, even colloidal particles with diameters on the order of 0.05to 1.0 microns, can not pass through the microporous layer because ofthe ultrafine pores. In contrast, for example, colloidal particles, suchas conductive carbon powders often incorporated into cathodecompositions of electrochemical cells, may readily pass throughconventional microporous layers, such as microporous polyolefins, andthereby may migrate to undesired areas of the cell.

Another significant advantage of the microporous layer comprising one ormore microporous xerogel layers of the methods of the present inventionis that the nanoporous structure of the xerogel layer may function as anultrafiltration membrane and, in addition to blocking all particles andinsoluble materials, may block or significantly inhibit the diffusion ofsoluble materials of relatively low molecular weights, such as 2,000 orhigher, while permitting the diffusion of soluble materials withmolecular weights below this cutoff level. This property may be utilizedto advantage in coating other layers onto the surface of the microporouslayer by preventing any undesired penetration of pigments and othermaterials into the microporous layer. For example, with electrochemicalcells, this property may also be utilized to advantage in selectivelyimpregnating or imbibing materials into the microporous separator layerduring manufacture of the electrochemical cell or in selectivelypermitting diffusion of very low molecular weight materials through themicroporous separator layer during all phases of the operation of thecell while blocking or significantly inhibiting the diffusion ofinsoluble materials or of soluble materials of medium and highermolecular weights.

Another important advantage of the extremely small pore diameters of themicroporous xerogel layer of the microporous layer of the methods of thepresent invention is the strong capillary action of the tiny pores inthe xerogel layer which enhances the capability of the microporouslayers to readily take up or imbibe liquids, such as electrolyte liquidsand ink jet ink liquids, and to retain these liquids in pores within themicroporous layer.

The microporous layers of the methods of this invention may optionallyfurther comprise a variety of binders (in addition to the binder, suchas for example a pseudo-boehmite xerogel, that provides the primarymicroporous structure of the separator layer), to improve the mechanicalstrength and other properties of the layer, as for example, describedfor microporous pseudo-boehmite xerogel layers for microporous separatorlayers in the two aforementioned copending U.S. patent application Ser.Nos. 08/995,089 and 09/215,112, both to Carlson et al. of the commonassignee. Any binder that is compatible with the microporous material ofthe microporous layer may be used. For microporous xerogel layers, anybinder that is compatible with the xerogel precursor sol during mixingand processing into the microporous xerogel layer and provides thedesired mechanical strength and uniformity of the layer withoutsignificantly interfering with the desired microporosity is suitable foruse. The preferred amount of binder is from 5% to 70% of the weight ofthe xerogel-forming material in the layer. Below 5 weight per cent, theamount of binder is usually too low to provide a significant increase inmechanical strength. Above 70 weight per cent, the amount of binder isusually too high and fills the pores to an excessive extent, which mayinterfere with the microporous properties and with the transport of lowmolecular weight materials through the layer. The binder may beinorganic, for example, another xerogel-forming material, such assilicas, gamma aluminum oxides, and alpha aluminum oxides, that areknown to be compatible with the primary xerogel-forming material, suchas pseudo-boehmite, present in the microporous layer, for example, as isknown in the art of ink-receptive microporous xerogel layers for ink jetprinting. In one embodiment, the binders in the microporous xerogellayer are organic polymer binders. Examples of suitable binders include,but are not limited to, polyvinyl alcohols, cellulosics, polyvinylbutyrals, urethanes, polyethylene oxides, copolymers thereof, andmixtures thereof. Binders may be water soluble polymers and may haveionically conductive properties. Suitable binders may also compriseplasticizer components such as, but not limited to, low molecular weightpolyols, polyalkylene glycols, and methyl ethers of polyalkylene glycolsto enhance the coating, drying, and flexibility of the microporousxerogel layer.

The thickness of the microporous layer of the methods of the presentinvention may vary over a wide range since the basic properties ofmicroporosity and mechanical integrity are present in layers of a fewmicrons in thickness as well as in layers with thicknesses of hundredsof microns. The microporous layer may be coated in a single coatingapplication or in multiple coating applications to provide the desiredoverall thickness. For various reasons including cost, overallperformance properties of the microporous layer, and ease ofmanufacturing, the desirable overall thicknesses of the microporouslayer are typically in the range of 1 micron to 25 microns.

In the methods of preparing an article of the present invention, thetemporary carrier substrate functions as a temporary support to thesuperposed layers during the process steps of this invention and may beany web or sheet material possessing suitable smoothness, flexibility,dimensional stability, and adherence properties in the microporous layerassembly. In one embodiment of the methods of preparing an article ofthe present invention, the temporary carrier substrate is a flexible websubstrate. Suitable web substrates include, but are not limited to,papers, polymeric films, and metals. A typical flexible polymeric filmfor use as the temporary carrier substrate is a polyethyleneterephthalate film. In a preferred embodiment, the flexible websubstrate is surface treated with a release agent to enhance desiredrelease characteristics, such as by treatment with a silicone releaseagent. This surface treatment or coating with a release agent of thetemporary carrier substrate may be done on a multistation coatingmachine in the same coating pass as that used to later apply the firstlayer of the microporous layer assembly in the methods of thisinvention. Examples of suitable flexible web substrates include, but arenot limited to, resin-coated papers such as papers on which a polymer ofan olefin containing 2 to 10 carbon atoms, such as polyethylene, iscoated or laminated; and transparent or opaque polymeric films such aspolyesters, polypropylene, polystyrene, polycarbonates, polyvinylchloride, polyvinyl fluoride, polyacrylates, and cellulose acetate. Thetemporary carrier substrate may be of a variety of thicknesses, such as,for example, thicknesses in the range of 2 to 100 microns.

One benefit is that the temporary carrier substrate, after its removalfrom the microporous layer/substrate assembly, may be reused forpreparing another article, may be reused for a different productapplication, or may be reclaimed and recycled. Any such reuses combineto lower the effective cost of the temporary carrier substrate inpreparing the article.

In a preferred embodiment of the methods of preparing an article of thepresent invention, the microporous layer comprises one or moremicroporous xerogel layers, and more preferably, the microporous layerassembly further comprises one or more non-microporous coating layers,wherein the one or more non-microporous coating layers are in contactwith at least one of the one or more microporous xerogel layers. In oneembodiment, one of the one or more microporous xerogel layers of themicroporous layer is coated directly on the temporary carrier substrate.In one embodiment, one of the one or more non-microporous coating layersof the microporous layer assembly is coated directly on the temporarycarrier substrate.

The incorporation of one or more non-microporous coating layers in themicroporous layer assembly of the methods of this invention may enhancethe mechanical strength and add flexibility to the microporous layercomprising one or more discrete microporous layers, particularly thosemicroporous layers comprising one or more microporous xerogel layers.The non-microporous coating layers may also provide specific functionalproperties to the article, such as adhesion to the substrate, ability toabsorb specific liquids, and specific gloss, opacity, and other opticalproperties. The thickness of the non-microporous coating layers of themicroporous layer assembly of the methods of this invention may varyover a wide range, such as, but not limited to, from 0.2 microns to 200microns.

To achieve the desired coating properties, the one or morenon-microporous coating layers may comprise polymers, pigments, andother materials known in the art of non-microporous coatings, especiallythose known for use in flexible and durable coatings. Examples of othercoating materials include, but are not limited to, photosensitizers forradiation curing of any monomers and macromonomers present; catalystsfor non-radiation curing of any monomers, macromonomers, or polymerspresent; crosslinking agents such as zirconium compounds, aziridines,and isocyanates; surfactants; plasticizers; dispersants; flow controladditives; and rheology modifiers.

The microporous layer assembly of the methods of the present inventionmay have more than one microporous layer. Also, the microporous layerassembly of the methods of the present invention may have more than onenon-microporous coating layer. The compositions of these multiplemicroporous layers may be the same or different for each such layer inthe microporous layer assembly. Also, the compositions of these multiplenon-microporous coating layers may be the same or different for eachsuch layer in the microporous layer assembly. The many possiblecombinations of microporous layers and non-microporous coating layersalso include a non-microporous coating layer intermediate between twomicroporous layers.

In one embodiment, the step of removing the temporary carrier substrateoccurs prior to or, alternatively, subsequent to a slitting step, forexample, as illustrated in FIGS. 2A and 2B. Referring to FIG. 2A, in alamination step 80, a substrate 401 is laminated to a microporous layerassembly 24 comprising a temporary carrier substrate 2, a microporouslayer 102, and two different non-microporous coating layers 201 and 301.This step 80 forms microporous layer/substrate assembly 27 comprisingsubstrate 401, non-microporous coating layers 201 and 301, microporouslayer 102, and temporary carrier substrate 2. Next, in a temporarycarrier substrate removing step 70, the temporary carrier substrate 2 isremoved from the microporous layer 102 of microporous layer/substrateassembly 27 to form article 28 comprising substrate 401, non-microporouscoating layers 201 and 301, and microporous layer 102. If a smallerdimension is desired for article 28, in a slitting step 95, article 28may be cut or slit to form multiples of article 32 comprising substrate401, non-microporous coating layers 201 and 301, and microporous layer102. Referring to FIG. 2B, this is similar to FIG. 2A except that thesequence of the slitting step 95 and the temporary carrier substrateremoving step 70 are reversed. In both FIG. 2A and FIG. 2B, the finalproduct is article 32.

The various coating layers in the methods of preparing a microporouslayer assembly of the present invention may be coated from a liquidmixture comprising a liquid carrier medium and the solid materials ofthe layer which are dissolved or dispersed in the liquid carrier medium.The choice of the liquid carrier medium may vary widely and includeswater, organic solvents, and blends of water and organic solvents.Exemplary organic solvents include, but are not limited to, alcohols,ketones, esters, and hydrocarbons. The choice of the liquid carriermedium depends mainly on the compatibility with the particular solidmaterials utilized in the specific coating layer, on the type of methodof coating application to the receiving surface, and on the requirementsfor wettability and other coating application properties of theparticular receiving surface for the coating. For example, for coating amicroporous xerogel layer, the liquid carrier medium is typically wateror a blend of water with an alcohol solvent, such as isopropyl alcoholor ethyl alcohol, since the sol-gel materials that dry and condense toform the xerogel layer typically are most compatible with a water-based,highly polar liquid carrier medium.

The application of the liquid coating mixture to the temporary carriersubstrate or other layer may be done by any suitable process, such asthe conventional coating methods, for example, of wire-wound rodcoating, spray coating, spin coating, reverse roll coating, gravurecoating, slot extrusion coating, gap blade coating, and dip coating. Theliquid coating mixture may have any desired solids content that isconsistent with the viscosity and rheology that is acceptable in thecoating application method. After the liquid coating mixture is appliedon the temporary carrier substrate or other layer, the liquid carriermedium is typically removed to provide a dried, solid coating layer.This removal of the liquid carrier medium may be accomplished by anysuitable process, such as conventional methods of drying, for example,hot air at a high velocity or exposure to ambient air conditions. Somelayers of the microporous layer assembly of the present invention suchas, for example, non-microporous current collector layers, may be formedby techniques such as vacuum deposition, ion-sputtering, vacuum flashevaporation, and other methods as known in the art.

A wide variety of articles comprising a microporous layer may beprepared by utilizing the methods of the present invention. Suitablearticles for preparation by the methods of this invention include, butare not limited to, electrochemical cells, capacitors, fuel cells, inkjet printing and other imaging media, and filtration media. In the caseof electric current producing articles such as electrochemical cells,capacitors, and fuel cells, which typically have two electrodes and amicroporous separator or membrane layer interposed between the twoelectrodes, the microporous layer assembly may be a firstelectrode/separator assembly, the substrate may be a second electrodeassembly such as a second electrode on a second temporary carriersubstrate, and the article may be the electrochemical cell, capacitor,or fuel cell depending on the specific electrodes, separator, and othercomponents utilized, as known in the art of these various electriccurrent producing articles. Alternatively, the microporous layerassembly may be a separator assembly, the substrate may be a firstelectrode assembly such as a cathode assembly or an anode assembly, andthe article may be a first electrode/separator assembly such as acathode/separator assembly.

For ink jet printing media, the microporous layer assembly may be an inkjet ink-receptive coating assembly such as one of the single or multiplecoating layer designs comprising a microporous layer as known in the artof ink jet printing media, the substrate may be a flexible web substratesuch as cloth, canvas, paper, and non-woven plastics, and the article isan ink jet printing media.

For filtration media, the microporous layer assembly may be anultrafiltration layer assembly such as a single or multiple coatinglayer designs comprising at least one microporous layer as known in theart of filtration media, the substrate may be a flexible web substratesuch as a paper, and the article is a filtration media. The methods ofthis invention are particularly advantageous for preparing filtrationmedia since the ultrafiltration properties of a microporous xerogellayer may be placed next to the paper surface by the lamination step tothe rough surface of the paper with the option of coarser filtrationlayers on the side of the xerogel layer opposite to the paper. Directcoating of the microporous xerogel layer on the rough paper substratestypically used in filtration media would be extremely difficult toachieve if the full ultrafiltration properties of the xerogel layer arerequired.

Another aspect of the present invention pertains to articles preparedaccording to the methods of the present invention, as described herein.Thus, the articles of the present invention comprise a microporouslayer, which articles are prepared according to the methods of thisinvention. Examples of such articles include, but are not limited to,electrochemical cells, ink jet printing media, filtration media,electrode/separator assemblies, capacitors, and fuel cells, as describedherein.

EXAMPLES

Several embodiments of the present invention are described in thefollowing example, which are meant by way of illustration and not by wayof limitation.

Example 1

A coating mixture for a microporous ink jet ink-receptive layer wasprepared by adding 23.8 g of a 13.5% by weight solids solution ofboehmite sol in water (DISPAL 11N7-12, a trademark for aluminum boehmitesols available from CONDEA Vista company, Houston, Tex.) to 14.2 g of a4% by weight solution of polyvinyl alcohol (AIRVOL 125, a trademark forpolyvinyl alcohol polymers available from Air Products, Inc. Allentown,Pa.) in water and stirring to mix the materials. 0.05 g of FLUORADFC-430, a trademark for non-ionic fluorochemical surfactants availablefrom 3M Corporation, St. Paul, Minn., was added with stirring to makethe final microporous coating mix. Using a gap coating with a doctorblade and a hand coating process, the microporous coating mix wasapplied to the non-treated surface of 23 micron thick MELINEX 6328, atrademark for polyethylene terephthalate (PET) films available fromDuPont Teijin Films, Wilmington, Del. After air drying in a laboratoryhood under a high rate of air circulation, a smooth and uniformmicroporous ink jet ink-receptive layer with a dry thickness of 14microns was formed on the PET film substrate.

A non-microporous coating layer of polyethylene oxide (900,000 MW fromAldrich Chemical Company, Milwaukee, Wis.) was prepared by coating a 2%by weight solution in water onto the microporous ink jet ink-receptivelayer using the gap coating bar with a doctor blade. After drying at130° C. in a convection oven, a uniform non-microporous coating layerwith a dry thickness of 5 microns was formed on the microporous layer.

The resulting microporous layer assembly of PET film as the temporarycarrier substrate, the microporous ink jet ink-receptive layer, and thenon-microporous coating layer was then laminated to a sheet of standardgrade xerographic bond paper by using a pressure roller process with thesurface of the non-microporous coating layer in contact to the paper.Following this lamination step, the PET film, which had a low level ofadhesion to the microporous layer, was easily removed by delaminationand peeling off the PET film. The resulting ink jet printing mediaarticle comprising the paper substrate, the non-microporous coatinglayer, and the microporous ink jet ink-receptive layer on its outersurface with the non-microporous coating layer now interposed betweenthe microporous layer and the substrate, was imaged on an HP 861 colorink jet ink printer (a trademark for products from Hewlett PackardCorporation, Palo Alto, Calif.). The resulting color quality and rate ofdrying of the ink was excellent. Because the top surface of themicroporous layer had orginally been coated on the smooth PET film, thistop surface of the microporous layer was very smooth and had a highgloss, which is a very desirable feature for ink jet printing,particularly for digital photographic applications.

While the invention has been described in detail and with reference tospecific and general embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

1. Filtration media comprising a microporous layer, wherein saidfiltration media is prepared according to a method comprising the stepsof: (a) coating a microporous layer on a temporary carrier substrate toform a microporous layer assembly, wherein said microporous layer has afirst surface in contact with said temporary carrier substrate and has asecond surface on the side opposite from said temporary carriersubstrate; (b) laminating said microporous layer assembly on the sideopposite from said temporary carrier substrate to a porous substrate toform a porous substrate/microporous layer assembly; (c) removing saidtemporary carrier substrate from said first surface of said microporouslayer.
 2. The filtration media of claim 1, wherein said microporouslayer comprises one or more microporous xerogel layers formed by dryinga liquid metal oxide sol to form a xerogel layer of a solid metal oxidegel matrix with pores which are interconnected in a continuous fashionfrom one outermost surface of said xerogel layer through to the otheroutermost surface of said xerogel layer.
 3. The filtration media ofclaim 1, wherein said microporous layer comprises one or moremicroporous metal oxide xerogel layers, wherein said microporous metaloxide xerogel layers are continuous xerogel coating layers with saidmetal oxides in a continuous structure in said xerogel coating layers.4. The filtration media of claim 2, wherein at least one of said one ormore microporous xerogel layers comprises a material selected from thegroup consisting of pseudo-boehmites, zirconium oxides, titanium oxides,aluminum oxides, silicon oxides, and tin oxides.
 5. The filtration mediaof claim 2, wherein said liquid metal oxide sol comprises a binderselected from the group consisting of organic polymer binders andinorganic binders.
 6. The filtration media of claim 3, wherein at leastone of said one or more microporous metal oxide xerogel layers comprisesa material selected from the group consisting of pseudo-boehmites,zirconium oxides, titanium oxides, aluminum oxides, silicon oxides, andtin oxides.
 7. The filtration media of claim 3, wherein at least one ofsaid one or more microporous metal oxide xerogel layers comprises abinder selected from the group consisting of organic polymer binders andinorganic binders.
 8. The filtration media of claim 1, wherein saidmicroporous layer comprises a discontinuous layer that is not a xerogelcoating layer and has discontinuities of solid pigment particles thatare separated from each other in the structure of said discontinuouslayer.
 9. The filtration media of claim 8, wherein said discontinuouslayer comprises a binder selected from the group consisting of organicpolymer binders and inorganic binders.
 10. The filtration media of claim1, wherein said temporary carrier substrate is a flexible web substrate.11. The filtration media of claim 10, wherein said flexible websubstrate is selected from the group consisting of papers, polymericfilms, and metals.
 12. The filtration media of claim 10, wherein saidflexible web substrate is surface treated with a release agent. 13.Filtration media comprising a microporous layer, wherein said filtrationmedia is prepared according to a method comprising the steps of: (a)coating a microporous layer on a temporary carrier substrate to form amicroporous layer assembly, wherein said microporous layer has a firstsurface in contact with said temporary carrier substrate and has asecond surface on the side opposite from said temporary carriersubstrate; (b) coating an overlying layer on said microporous layerassembly on the side opposite from said temporary carrier substrate; (c)laminating said overlying layer to a porous substrate to form a poroussubstrate/microporous layer assembly; (d) removing said temporarycarrier substrate from said first surface of said microporous layer. 14.The filtration media of claim 13, wherein said microporous layercomprises one or more microporous xerogel layers formed by drying aliquid metal oxide sol to form a xerogel layer of a solid metal oxidegel matrix with pores which are interconnected in a continuous fashionfrom one outermost surface of said xerogel layer through to the otheroutermost surface of said xerogel layer.
 15. The filtration media ofclaim 13, wherein said microporous layer comprises one or moremicroporous metal oxide xerogel layers, wherein said microporous metaloxide xerogel layers are continuous xerogel coating layers with saidmetal oxides in a continuous structure in said xerogel coating layers.16. The filtration media of claim 14, wherein at least one of said oneor more microporous xerogel layers comprises a material selected fromthe group consisting of pseudo-boehmites, zirconium oxides, titaniumoxides, aluminum oxides, silicon oxides, and tin oxides.
 17. Thefiltration media of claim 14, wherein said liquid metal oxide solcomprises a binder selected from the group consisting of organic polymerbinders and inorganic binders.
 18. The filtration media of claim 15,wherein at least one of said one or more microporous metal oxide xerogellayers comprises a material selected from the group consisting ofpseudo-boehmites, zirconium oxides, titanium oxides, aluminum oxides,silicon oxides, and tin oxides.
 19. The filtration media of claim 15,wherein at least one of said one or more microporous metal oxide xerogellayers comprises a binder selected from the group consisting of organicpolymer binders and inorganic binders.
 20. The filtration media of claim13, wherein said microporous layer comprises a discontinuous layer thatis not a xerogel coating layer and has discontinuities of solid pigmentparticles that are separated from each other in the structure of saiddiscontinuous layer.
 21. The filtration media of claim 20, wherein saiddiscontinuous layer comprises a binder selected from the groupconsisting of organic polymer binders and inorganic binders.
 22. Thefiltration media of claim 13, wherein said temporary carrier substrateis a flexible web substrate.
 23. The filtration media of claim 22,wherein said flexible web substrate is selected from the groupconsisting of papers, polymeric films, and metals.
 24. The filtrationmedia of claim 22, wherein said flexible web substrate is surfacetreated with a release agent.
 25. Filtration media comprising amicroporous layer, wherein said filtration media is prepared accordingto a method comprising the steps of: (a) coating a microporous layer ona temporary carrier substrate to form a microporous layer assembly,wherein said microporous layer has a first surface in contact with saidtemporary carrier substrate and has a second surface on the sideopposite from said temporary carrier substrate; (b) removing saidtemporary carrier substrate from said first surface of said microporouslayer to form a free standing microporous layer; (c) laminating saidfree standing microporous layer to a porous substrate.
 26. Thefiltration media of claim 25, wherein said microporous layer comprisesone or more microporous xerogel layers formed by drying a liquid metaloxide sol to form a xerogel layer of a solid metal oxide gel matrix withpores which are interconnected in a continuous fashion from oneoutermost surface of said xerogel layer through to the other outermostsurface of said xerogel layer.
 27. The filtration media of claim 25,wherein said microporous layer comprises one or more microporous metaloxide xerogel layers, wherein said microporous metal oxide xerogellayers are continuous xerogel coating layers with said metal oxides in acontinuous structure in said xerogel coating layers.
 28. The filtrationmedia of claim 26, wherein at least one of said one or more microporousxerogel layers comprises a material selected from the group consistingof pseudo-boehmites, zirconium oxides, titanium oxides, aluminum oxides,silicon oxides, and tin oxides.
 29. The filtration media of claim 26,wherein said liquid metal oxide sol comprises a binder selected from thegroup consisting of organic polymer binders and inorganic binders. 30.The filtration media of claim 27, wherein at least one of said one ormore microporous metal oxide xerogel layers comprises a materialselected from the group consisting of pseudo-boehmites, zirconiumoxides, titanium oxides, aluminum oxides, silicon oxides, and tinoxides.
 31. The filtration media of claim 27, wherein at least one ofsaid one or more microporous metal oxide xerogel layers comprises abinder selected from the group consisting of organic polymer binders andinorganic binders.
 32. The filtration media of claim 25, wherein saidmicroporous layer comprises a discontinuous layer that is not a xerogelcoating layer and has discontinuities of solid pigment particles thatare separated from each other in the structure of said discontinuouslayer.
 33. The filtration media of claim 32, wherein said discontinuouslayer comprises a binder selected from the group consisting of organicpolymer binders and inorganic binders.
 34. The filtration media of claim25, wherein said temporary carrier substrate is a flexible websubstrate.
 35. The filtration media of claim 34, wherein said flexibleweb substrate is selected from the group consisting of papers, polymericfilms, and metals.
 36. The filtration media of claim 34, wherein saidflexible web substrate is surface treated with a release agent.